This invention relates to a method of purifying 1,1-dichloro-1-fluoroethane by removal of unsaturated carbon compounds such as vinylidene chloride having the same or similar boiling points.
In the prior art, 1,1-dichloro-1-fluoroethane, sometimes referred to by the designation HCFC-141b, has been prepared by the reaction of vinylidene chloride with hydrogen fluoride. Often after the reaction, traces of unreacted vinylidene chloride, as well as various other unsaturated organic impurities, remain in the 1,1-dichloro-1-fluoroethane and cannot be easily separated therefrom by distillation or other means because they have similar boiling points. Vinylidene chloride has a boiling point of 31.7.degree. C. and 1,1-dichloro-1-fluoroethane has a boiling point of 32.1.degree. C., and thus they are difficult to separate by distillation. It is particularly desirable to remove vinylidene chloride because it is toxic and is considered to be a carcinogen.
Various methods have been proposed for removing unsaturated organic compounds, such as vinylidene chloride from saturated hydrohalofluorocarbons. For example, U.S. Pat. No. 5,105,035 discloses a process for removing vinylidene chloride and other unsaturated impurities film HCFC-141b by reaction with hydrogen over a catalyst such as palladium on alumina. However, this process can result in a loss of HCFC-141b by dechlorination which results from excessive hydrogenation and hydrodechlorination.
U.S. Pat. No. 5,300,714 discloses a method of removing olefinic impurities, such as perfluoroisobutylene, from fluoroperhalocarbon liquid, such as perfluorinated liquid. The method comprises the step of contacting the fluoroperhalocarbon liquid with a body of particles comprising particles selected from the group consisting of alumina, alkali alumina, alkali metal hydroxide, alkaline earth oxide, alkaline earth hydroxide, silicon oxide, tin oxide, zinc oxide, alkaline earth basic carbonate, and alkaline earth basic phosphate, transition alumina particles and mixtures thereof.
European Patent 39311839 (1989) discloses purification of saturated fluorohalocarbons containing unsaturated impurities by the use of aluminas to oxidize unsaturated impurities to carbon dioxide.
U.S. Pat. No. 4,754,088 discloses a process for oxychlorination of ethylene wherein 1,2-dichloroethane is prepared by chlorination of ethylene-containing reaction vent gases from the oxychlorination of ethylene in the presence of a catalyst carrier impregnated with metal compounds wherein the waste from the oxychlorination stage are chlorinated, the improvement comprising preheating the ethylene-containing waste gases to at least 50.degree. C. and then chlorinating the ethylene at 100.degree. to 300.degree. C. at a pressure of 1 to 7 bar with a space velocity of 100 to 5000 h.sup.-1 related to standard conditions in the presence of at least one metal compound selected from the group consisting of chlorides and oxides of manganese, nickel and cobalt supposed on a catalyst carrier with reduced formation of oxychlorinated by-products.
U.S. Pat. No. 4,329,323 discloses a process for removing ethylene and vinyl chloride from a gas stream containing them by passing a mixed gas containing ethylene, vinyl chloride and a necessary amount of chlorine through a fixed-bed reactor charged with, as a catalyst, an activated alumina supporting at least 4% by weight of chloride in terms of iron, the catalyst having an outer surface area per unit packed catalyst volume of not less than 7.8 cm.sup.2 /ml. Ethylene and vinyl chloride are converted into and removed as 1,2-dichloroethane and 1,1,2-trichloroethane. The concentrations of ethylene and vinyl chloride can be decreased to not more than 10 ppm and not more than 20 ppm, respectively.
U.S. Pat. No. 2,498,552 discloses a process for the chlorination of normally gaseous paraffinic hydrocarbons which comprises introducing the hydrocarbon to be chlorinated and chlorine into a chlorination zone, introducing cupric oxychloride into the chlorination zone, maintaining a temperature within the range of from about 325.degree. C. to about 500.degree. C. in the chlorination zone, regulating the rate of introduction of the cupric oxychloride so that at least one mole of oxychloride is introduced per mole of chlorine introduced thereto, and recovering the chlorinated hydrocarbons from the gaseous effluent from the chlorination zone.
U.S. Pat. No. 4,034,049 discloses meso-1,2,3,4-tetrachlorobutane produced in an improved liquid phase chlorination process wherein the trans-1,4-dichlorobutene-2 is contacted with chlorine in the presence of a catalytic amount of molybdenum.
U.S. Pat. No. 4,922,042 discloses a process for the production of 1,2-dichloroethane by the reaction between ethylene and chlorine in the vapor phase in the presence of a catalyst comprising alumina, wherein the reaction is carried out using a fluidized bed comprising fluidizable, substantially spherical particles of alumina of surface area not exceeding 10 m.sup.2 g.sup.-1 and especially in the range 0.2 to 6 m.sup.2 g.sup.-1.
British Patent 627,773 (1949) discloses the separation of 1,1-dichloro-1-fluoroethane from its admixture with vinylidene chloride by chlorination of the vinylidene chloride and recovery of the 1,1-dichloro-1-fluoroethane by distillation.
Poutsma et al in an article entitled "Chlorination Studies of Unsaturated Materials in Nonpolar Media. I. Solvent Effects on Radical Addition of Chlorine to Chloroethylenes" disclose that the relative rates of addition of chlorine atom to 1,1-dichloroethylene, cis- and trans-1,2-dichloroethylene, trichloroethylene, and tetrachloroethylene in noncomplexing solvents have been measured both directly by competitive photochlorination of pairs of olefins and indirectly by comparison of addition to each olefin in competition with hydrogen abstraction from cyclohexane. The selectivity of chlorine atom with respect to such radical addition has been found to be substantially increased by the presence of the complexing solvents benzene and carbon disulfide. Solvent dependence has also been demonstrated for the competition between addition to the olefins and hydrogen abstraction from cyclohexane; attempts to extend such solvent effects to competitive addition and abstraction behavior of the trichloromethyl radical were unsuccessful.
In spite of these prior processes, there is still a great need for an economic, efficient process that enables separation of vinylidene chloride, for example, from 1,1-dichloro-1-fluoroethane. The present invention provides such a process.